General features of Algae:

General features of Algae Can be microscopic or macroscopic: size ranges from bacteria size to 50 meters long!
Lack vascular (conducting) tissues – No xylem or phloem
No true roots, stems or leaves
Modes of sexual reproduction:
Both sexual and asexual
Algae illustrate the importance of photosynthesis to the Earth’s ecology!

Diversity of Algae:

Diversity of Algae There are millions of algal species, but we’ll focus in these five groups:
Diatoms
Dinoflagellates
Red Algae
Kelps or Brown Algae
Green algae

1. Diatoms:

1. Diatoms Diatoms: Division Bacillariophyta
Large group of algae (many unidentified). Relatively recently evolved group
Habitat: Diatoms live in cool oceans
Structure: mostly unicellular, have silica in their cell walls

Diatoms:

Diatoms Very important for aquatic food chains: they provide phytoplankton
sun
Phytoplankton  Zooplankton  small fish  larger fish mollusks whales
Can reproduce asexually for many generations, then sexually

3. Red Algae:

3. Red Algae Red algae: Division Rhodophyta (4000 species)
Are some of the oldest eukaryotic organisms on earth (2 billion year old fossils)
Abound in tropical, warm waters
Act as food and habitat for many marine species
Structure: from thin films to complex filamentous membranes

Why are Red algae red?:

Why are Red algae red? Accessory pigments! Phycobilins mask the Chlorophyll a – thus they look red.
Due to these accessory pigments, red algae can photosynthesize in deeper waters (at different light wavelengths).

Red algae:

Red algae Commercial uses: Carrageenan used for making ice cream, jellies, syrups, breads.
Also for lotions, toothpaste, pharmaceutical jellies.
Agar for growing bacteria and fungi for research purposes.
As food.

4. Kelps or Brown Algae:

4. Kelps or Brown Algae Kelps: Division Phaeophyta
Closely related to diatoms, also a recent group… but look very different from diatoms!
Habitat: rocky coasts in temperate zones or open seas (cold waters)
Structure: multicellular only
Holdfast, stipe, blade, air bladder
Up to 50 meters long

5. Green Algae:

5. Green Algae Division: Chlorophyta
Largest and most diverse group of algae
Habitat: found mostly in fresh waters and on land.
Float in rivers, lakes, reservoirs, creeks.
Can also live on rocks, trees, soil

Green algae:

Green algae:

Green algae Terrestrial plants arose from a green algal ancestor
Both have the same photosynthetic pigments (Chlorophyll a and b).
Some green algae have a cell wall made of cellulose
Cells divide similarly

Benefits of Algae:

Benefits of Algae Beneficial algae:
They are the base of the aquatic food chain – photosynthetic organisms
Lichens: algae and fungi symbiosis
Also serve as shelters: Kelps form underwater forests; red alga form reefs

Harmful algae:

Harmful algae Excessive growth of algae causes:
Clogging of water ways, streams, filters… makes the water taste bad.
Can be toxic to animals
“Red tides” caused by dinoflagellates

Kingdom Plantae:

Kingdom Plantae When moving from water to land, both plants and animals faced the same challenges, but evolved different ways to deal with them

Plants evolved from algae:

Plants evolved from algae Algae cannot survive on land (only in moist environments)
Plants had to adapt (evolve) characteristics that would allow them to survive and live on dry land
Cooksonia is the earliest known land plant (fossil)
It’s non-vascular and similar to today’s bryophytes

Ancestor of plants: Green Algae:

Ancestor of plants: Green Algae The ancestor of land plants was probably a green alga: something like modern Coleochaete
1. They both have same photosynthetic pigments (Chlorophyll a & b, carotenes, etc.)
2. Both use starch to store photosynthetic products
3. Both have cellulose in their wall
4. Both have ‘alternation of generations’…
5. Both form a cell plate during cell division

Kingdom Plantae:

Living on land:

Living on land Several environmental challenges had to be met by early plants in order to live on land…
A. OBTAINING ENOUGH WATER
Plants evolved roots to anchor the plant
Roots to absorb water and dissolved minerals

C. GETTING ENOUGH ENERGY:

C. GETTING ENOUGH ENERGY In land, plants obtained enough sunlight for photosynthesis
Different strategies for obtaining light:
Growing taller and above other plants – plants began to evolve support cells
Others had to adapt to lower light intensities

D. Photosynthesis/water dilemma:

D. Photosynthesis/water dilemma Problems – plants need pores for gas exchange for photosynthesis, but open pores (stomata) allow water to leave (95% water taken is lost)
Solution – stomata open during the day (for photosynthesis gas exchange) and close during the night (to allow plant to recover from water loss)

Life cycles: animals vs. plants:

Plant life cycle: alternation of generations:

Plant life cycle: alternation of generations Plants spend part of their life cycle in the haploid (1 n) stage, and part in the diploid (2 n) stage – both stages are multicellular Sporophyte generation (2n) Gametophyte generation (1n)

Slide31:

Plants display an alternation of haploid and diploid phases in their life cycle.
(see text and image on page 139 in the textbook “Plants and Society”)

Bryophytes:

Bryophytes Sporocytes within the Sporophyte undergo meiosis to produce a single kind of haploid spore
If spore lands on suitable place, it will germinate into a protonema, the initial stage of the gametophyte plant.

Bryophyte significance:

Bryophyte significance Bryophytes are small and inconspicuous, but important part of the biosphere
Food for mammals, birds
Important to prevent soil erosion along streams
Commercially – peat moss (Sphagnum) is used as fuel, soil conditioner, by florists

FERNS:

FERNS An important group of plants – 10,000 species exist
Ferns have developed vascular tissue
Habitat: Moist tropics, woodlands, streambanks
Also exhibit Alternation of Generations, but…
The diploid Sporophyte generation is dominant (larger and more visible)
The haploid Gametophyte is small & short lived.

Fern life cycle: dominant sporophyte:

Fern life cycle: dominant sporophyte Sporophyte generation (diploid) is dominant, larger
Sporophyte has well developed vascular system (xylem, phloem)
(See image on page 141 of the textbook please)

Fern sporophyte morphology:

Fern sporophyte morphology Fern sporophyte has fronds (leaves)
Young fronds are called fiddleheads They also have an underground horizontal stem called the rhizome True roots arise from the rhizome

Fronds:

Fronds Ferns have complex leaves called fronds, for photosynthesis and reproduction
Under the fronds, spores are produced in sporangia in clusters called sori (sorus = singular)
In sporangia, meiosis occurs producing haploid spores

Fern Gametophyte generation (1n):

Fern Gametophyte generation (1n) Single spore grows into the gametophyte plant
Heart-shaped called prothallus, very small.
Archegonia and antheridia produced in prothallus
Female gametophytes produce a chemical that induces spores to produce male gametophytes around it

Fern gametophyte :

Fern gametophyte Antheridium produces motile sperm that swim to the archegonia’s egg – fusion occurs and the diploid sporophyte generation begins
Zygote develops into a new embryo – that eventually grows into mature sporophyte